The recovery of mineral acids from mixtures is generally known. B. A. Bolto and L. Pawlowski, Wastewater Treatment by Ion Exchange, pp. 49-56 (E. & F. N. Spoon, Ltd, N.Y., N.Y., 1987), describe the use of ion exchange resins to separate acids from salts by acid retardation, e.g. the separation of iron sulfate salts from sulfuric acid in exhausted steel pickling solutions. Bolto also states that ion-exchange methods can be use for the recovery of various organic compounds from wastes, citing for example, the separation of sulphonic and sulfuric acids. Bolto cites as an example the separation of 5-sulfoisophthalic acid from sulfuric acid as described by R. C. Glogau, "Separate Sulfonic and Sulfuric Acids with an Ion Exchange Resin", Industrial and Engineering Chemistry, vol. 53, pp. 275-278 (April 1961).
Glogau et al. states that the separations of sulfuric acid from 5-sulfoisophthalic acid, from benzenesulfonic acid and from p-toluenesulfonic acid were studied. Most of the work was done with 5-sulfoisophthalic acid and Dowex 1-X16. Glogau et al. state they studied the effect of degree of crosslinking of the resin from Dowex 1-X7.5 to 1-X24 (i.e. from 7.5% to 24% divinylbenzene crosslinking agent) and found that acid capacity decreased with increasing crosslinking and in several cases the 5-sulfoisophthalic acid was virtually excluded.
An early Dow technical bulletin, "Chemical Processing By Ion Exchange", Form No. 17 424, pp. 1-18 (Dow Chemical U.S.A., Midland, Mich.) describes, at page 2, the Dowex 1 series of resins as Type I strong base anion exchange resins. The Dow bulletin further states that the Dowex 1 series is of the gel type made from styrene and divinyl benzene. The Dow bulletin discusses acid retardation at pages 12 and 13. It is stated that acid retardation permits separation of strong acids from their salts by passing the solution through the corresponding salt from of Dowex 1X8 or Dowex 21K, strong base anion exchange resin, for example passing a strong solution of hydrochloric acid and sodium chloride through the chloride form of Dowex 1X8. The Dow bulletin goes on to state at page 13 that the procedure has been used to separate free sulfuric acid from sulfonated oils, particularly when more highly crosslinked resins are used.
A later Dow technical bulletin, "Dowex Ion Exchange Resins; Powerful Chemical Processing Tools", Form. No. 177-1395-87, pp. 1-12 (Dow Chemical U.S.A., Midland, Mich.) notes at page 9 that mixtures of sulfuric acid and its salts are separated by passage through a bed of Dowex M-41 resin which selectively imbibes the acid moiety relative to the salt. Dowex M-41 is a type I strongly basic anion exchange resin having a macroreticular (or macro-porous) structure. (Macroreticular is a term employed in literature from Rohm & Haas regarding ion exchange resins; the term "macroporous" is employed by most other manufacturers of ion exchange resins.)
British Patent GB-1,264,293 describes the use of macro-reticular ion exchange resins to remove sulfuric acid from oil-soluble sulfonic acids. It is stated at page 2, lines 4-14, that the process is restricted to the oil-soluble sulfonic acids and that such acids, in order to be considered oil-soluble, generally require that the hydrocarbon portion of the sulfonic acid have a molecular weight between 350 and 1,000, and that examples of the oil-soluble sulfonic acids are alkaryl hydrocarbons having the required molecular weight, e.g. those derived from benzene, toluene, xylene or naphthalene. In the process, the oil-soluble sulfonic acid is in a hydrocarbon solvent and regeneration of the resin is accomplished by washing with water.